Field Continuity Testing Assistance

Wed Aug 24, 2011 2:10 pm

The following is the field unit from a DeWalt 402 angle grinder:

You will notice on the right side 2 connecting points. There is continuity between those connections.On the left, there is one connector and one open slot. I'm assuming the slot is for a grounding spade from the switch assembly. There is no continuity between the connector and slot, nor is there continuity between the connector and field core itself. I do,however, get continuity from the connector to the blob of solder on the field winding (previous repair). This leaves me with some questions:

1. Is one of the field windings normally connected (grounded?) to the field core 2. If not, does continuity then depend on a different ground 3. Were I to make a connection from the solder on the field winding directly to the field core, would this repair the field and allow SAFE operation of the tool?4. If not, may I assume the field is no longer repairable and should be replaced

I hate to toss a possibly repairable tool, but I don't want my ignorance to compromise my safety.

Add'l info: There are 2 line connections and 2 brush connections to the above field unit.

Re: Field Continuity Testing Assistance

Wed Aug 24, 2011 3:08 pm

I have never seen a Dewalt field so just guessing. There should never be continuity between the field windings and the iron core. Just check it with an ohm meter and I expect there will be continuity between the field connections and the iron core. If that is the case I would not use the unit.

I am assuming the brush connectors go to the fields at an angle, i.e. top left to bottom right or top right to bottom left. The line in wires just the opposite. There should be no continuity to the bottom left since that is just a piece of plastic. That is where the soldered wire originally went. There should be continuity between the two top terminals and no where else. Also continuity between the bottom terminal and the soldered wire and no where else. If you have continuity between the iron core and any of the terminals then you have a short and using the tool would be a bad idea. Continuity between the two right terminals or between the left terminal and the soldered wire is also an indication that there is a short somewhere.

When I was young, someone gave me an drill made by the A.C. Gilbert company that made Erector sets and chemistry sets. It looked like a round can which was the motor with a simple handle on the bottom. The handle screw was missing so I put a wood screw in its place. Seemed to fit well but the drill would only work if I pushed on the screw head with my finger. I used the drill many times like that until one day I got a good shock. The longer wood screw went inside the case and was screwed into one of the field winding which cut some of the wires. Pushing on the screw head allowed the screw to conduct electrons connecting the cut wires but also connected the metal case and my body to the line voltage. Well, I was just a young kid so I wrapped the drill handle and body with friction tape and continued to use the drill for several years after.

Re: Field Continuity Testing Assistance

Wed Aug 24, 2011 8:07 pm

Looking at that glob of solder, lower left corner of the field winding. Without closer inspection - looks like some of the windings are shorted out/together. Also looks like some of the coating on the copper wire has been scraped off.

Any way. My recent experience with DeWalt is that it's usually costs a bit more to purchase a new contractor grade tool than the repair parts. And you get a warranty.

Edit: Check you local big box store flyers for sales on DeWalt equipment.

Re: Field Continuity Testing Assistance

Thu Aug 25, 2011 6:47 am

Thank you Landreo and Eugene. Looks like I'm missing a connector that belongs in that open slot. Now that I think of it, the original repair was to reattach the wire from that connector to the field winding. Oh well, got another year out of that repair Time for a new one Thanks for mitigating my ignorance and saving me a BIG surprise

Eugene, that glob of solder was coated with superglue after the repair to properly insulate it.

Re: Field Continuity Testing Assistance

Thu Aug 25, 2011 8:52 am

Bill E Bob wrote:Eugene, that glob of solder was coated with superglue after the repair to properly insulate it.

People just don't know how to repair things any more. Back in the old days it would have been covered with a piece of friction tape.